The present invention relates generally to stoves and cooking apparatus for use in confined areas.
About half of the world's population cooks over a biomass fire. Use of biomass as an energy source has lead to deforestation as well as a decrease in indoor air quality. In Africa, this biomass fuel source is typically charcoal.
Charcoal stoves may burn relatively smoke free (i.e. low production of particulate matter), however they tend to produce high levels of carbon monoxide (CO). This may be caused by inefficient or incomplete combustion of charcoal fuel. While production of CO may not pose a significant problem when cooking in open spaces, such as out of doors, when charcoal combustion takes place within a living space or other enclosed space, carbon monoxide may build-up causing sickness or death.
Carbon monoxide is a colorless, odorless, tasteless toxic gas produced by incomplete combustion in fuel-burning. CO poisoning may result in headaches, nausea, dizziness, or confusion. Left undetected, CO exposure can be fatal, and in the United States alone, accidental CO poisoning results in about 15,000 ER visits a year.
Because carbon monoxide is a byproduct of incomplete combustion, procedures that enhance combustion will reduce the production of carbon monoxide. Those of skill in the art will understand that enhancing combustion may generally be accomplished in at least three ways—by increasing the duration of combustion, raising the temperature at which combustion takes place, or optimizing the mixing of oxygen and fuel.
In some cases, maximizing one factor may lead to minimization of a second factor. For example, optimizing the mixing of oxygen often requires maximizing airflow, but this may also lead to a decrease in combustion temperature as cooler ambient air enters the combustion area. Thus, enhancement of combustion often requires a balancing of these factors.
It is easier to control the factors that enhance combustion when the fuel source is gaseous rather than solid. Developed countries have largely replaced solid fuel with gaseous fuels for cooking and heating. But, as is evident from the CO poisoning statistics presented above, the use of gaseous fuels alone will not prevent CO poisoning when fuels are burned indoors.
Modern appliances are often controlled by sophisticated electronics, and combustion products are normally vented directly out of the living space to help reduce CO production and/or buildup. In contrast, in developing countries where charcoal combustion may take place on simple cookstoves, within the living space, and with little or no dedicated ventilation, stoves should be engineered to balance efficiency and CO production.
Reducing CO emission may require both a reduction in the production of CO as well as combustion of any CO that is produced.
Fuel burn rate, airflow rate, and operating temperature are some of the most important and basic characteristics of a stove. Charcoal stoves generally operate at higher temperatures than other biomass stoves. The top of a charcoal fuel bed may be about 1000° K [˜730° C.]. CO oxidation is affected by combustion temperature, residency time, and oxygen concentration.
In many rural and developing communities, especially in Africa and Asia, charcoal is a major energy source. Charcoal is made by partially cooking biomass, such as wood, in a low oxygen environment. This process, often referred to as pyrolysis, reduces the water and volatile content of the biomass rendering it mostly carbon. Charcoal burns at very high temperatures. In some cases, charcoal may burn at or about 1100° C.
Even before charcoal is used as an energy source, production of charcoal contributes to deforestation and increases greenhouse gases (both from direct production of charcoal and as an indirect result of loss of trees). Thus an increase in the efficiency of charcoal stoves may decrease the need for charcoal with an accompanying decrease in deforestation and greenhouse gases.
Existing charcoal stove designs, for the most part, rely on traditional materials such as brick, stone, or ceramics, while some stoves may also be constructed of metal. Mass produced ceramic stoves may have increased efficiency over traditional charcoal stove designs, but ceramic stoves tend to have high production and distribution costs due to the time needed to construct them (e.g. casting, drying, and firing) and their weight. Metal stoves may be lighter weight and rapidly constructed, but metal stoves are usually less-efficient than ceramic stoves due to quenching of the combustion temperature. In addition, some metal combustion chambers may be more susceptible to corrosion.
Many manufactured stoves, designed for use with solid biomass fuels, are not specifically designed to lessen production of dangerous combustion products. Those manufactured stoves that do address indoor pollution are generally not ideal, either because they rely on drastic changes in traditional behavior (such as limiting use of solid fuels, moving the stoves out of doors, or depending on expensive or impractical venting), or they are financially out of reach for the poor. A cooking/heating alternative that is compatible with traditional behavior, inexpensive, and capable of lessening production of dangerous gases, may help prevent death and disease especially among persons of limited income.
One example of a mass produced charcoal stove is the Jiko stove. Over one million Kenyan Ceramic Jiko (KCJ) stoves have been distributed in Kenya and East African nations. The Jiko stove, designed by Kenya Energy and Environment Organizations (KENGO), is ceramic and therefore difficult to manufacture and expensive to distribute. Moreover, while the Jiko stove has demonstrated a near doubling of thermal efficiency as compared to other typical African stoves, use of the Jiko stove results in little to no reduction in harmful emissions.
What is needed is a charcoal stove that lessens CO production while being efficient, inexpensive, and corrosion-resistant. A metal stove with these qualities may be inexpensively manufactured and distributed in rural and developing countries.